The present applicant has previously proposed in JP-A-2002-243690 a capacitance type humidity sensor having a moisture-sensitive film of which the specific inductivity varies depending upon the humidity interposed between a pair of electrodes.
The above capacitance type humidity sensor has a sensor unit which comprises a pair of electrodes formed like comb teeth on the same plane of a substrate, and a moisture-sensitive film formed so as to cover the pair of electrodes. Further, in order to detect fine variations in the capacitance maintaining good sensitivity, the above sensor has a C-V converter unit of a switched capacitor constitution. Therefore, when the specific inductivity of the moisture-sensitive film varies accompanying the change in the humidity and the capacitance varies between the pair of electrodes, the change in the capacitance is converted into a voltage through the C-V converter unit and is produced as a sensor output. The humidity is thus detected.
In the above constitution, however, when the moisture-sensitive film interposed between the pair of electrodes exhibits moisture absorbing/releasing properties that vary depending upon the temperature (i.e., temperature characteristics), the temperature characteristics appear in the change of capacitance of the sensor unit, too (temperature characteristics in the sensitivity). Namely, there appears a difference in the characteristics of the sensor output depending upon the temperature.
To correct the temperature characteristics, it can be contrived, for example, to provide a correction circuit for forming an adjusting voltage that varies depending upon the temperature in a stage subsequent to the C-V converter unit to adjust the deviation caused by the temperature characteristics. To form the adjusting voltage having temperature characteristics, however, it is necessary to separately provide a correction circuit portion of a complex circuit constitution, causing an increase in the chip areas and boosting up the cost. It is also possible to correct the temperature characteristics relying upon a complex digital signal processing, boosting, however, the cost, too.